Kubernetes is Moving on From Dockershim: Commitments and Next Steps

Authors: Sergey Kanzhelev (Google), Jim Angel (Google), Davanum Srinivas (VMware), Shannon Kularathna (Google), Chris Short (AWS), Dawn Chen (Google)

Kubernetes is removing dockershim in the upcoming v1.24 release. We're excited to reaffirm our community values by supporting open source container runtimes, enabling a smaller kubelet, and increasing engineering velocity for teams using Kubernetes. If you use Docker Engine as a container runtime for your Kubernetes cluster, get ready to migrate in 1.24! To check if you're affected, refer to Check whether dockershim removal affects you.

Why we’re moving away from dockershim

Docker was the first container runtime used by Kubernetes. This is one of the reasons why Docker is so familiar to many Kubernetes users and enthusiasts. Docker support was hardcoded into Kubernetes – a component the project refers to as dockershim. As containerization became an industry standard, the Kubernetes project added support for additional runtimes. This culminated in the implementation of the container runtime interface (CRI), letting system components (like the kubelet) talk to container runtimes in a standardized way. As a result, dockershim became an anomaly in the Kubernetes project. Dependencies on Docker and dockershim have crept into various tools and projects in the CNCF ecosystem ecosystem, resulting in fragile code.

By removing the dockershim CRI, we're embracing the first value of CNCF: "Fast is better than slow". Stay tuned for future communications on the topic!

Deprecation timeline

We formally announced the dockershim deprecation in December 2020. Full removal is targeted in Kubernetes 1.24, in April 2022. This timeline aligns with our deprecation policy, which states that deprecated behaviors must function for at least 1 year after their announced deprecation.

We'll support Kubernetes version 1.23, which includes dockershim, for another year in the Kubernetes project. For managed Kubernetes providers, vendor support is likely to last even longer, but this is dependent on the companies themselves. Regardless, we're confident all cluster operations will have time to migrate. If you have more questions about the dockershim removal, refer to the Dockershim Deprecation FAQ.

We asked you whether you feel prepared for the migration from dockershim in this survey: Are you ready for Dockershim removal. We had over 600 responses. To everybody who took time filling out the survey, thank you.

The results show that we still have a lot of ground to cover to help you to migrate smoothly. Other container runtimes exist, and have been promoted extensively. However, many users told us they still rely on dockershim, and sometimes have dependencies that need to be re-worked. Some of these dependencies are outside of your control. Based on your feedback, here are some of the steps we are taking to help.

Our next steps

Based on the feedback you provided:

  • CNCF and the 1.24 release team are committed to delivering documentation in time for the 1.24 release. This includes more informative blog posts like this one, updating existing code samples, tutorials, and tasks, and producing a migration guide for cluster operators.
  • We are reaching out to the rest of the CNCF community to help prepare them for this change.

If you're part of a project with dependencies on dockershim, or if you're interested in helping with the migration effort, please join us! There's always room for more contributors, whether to our transition tools or to our documentation. To get started, say hello in the #sig-node channel on Kubernetes Slack!

Final thoughts

As a project, we've already seen cluster operators increasingly adopt other container runtimes through 2021. We believe there are no major blockers to migration. The steps we're taking to improve the migration experience will light the path more clearly for you.

We understand that migration from dockershim is yet another action you may need to do to keep your Kubernetes infrastructure up to date. For most of you, this step will be straightforward and transparent. In some cases, you will encounter hiccups or issues. The community has discussed at length whether postponing the dockershim removal would be helpful. For example, we recently talked about it in the SIG Node discussion on November 11th and in the Kubernetes Steering committee meeting held on December 6th. We already postponed it once in 2021 because the adoption rate of other runtimes was lower than we wanted, which also gave us more time to identify potential blocking issues.

At this point, we believe that the value that you (and Kubernetes) gain from dockershim removal makes up for the migration effort you'll have. Start planning now to avoid surprises. We'll have more updates and guides before Kubernetes 1.24 is released.